Abstract The photoelectrical properties of two dyes—ethyl red and carminic acid—as sensitizers of dye-sensitized solar cells were investigated in experiments herein described. In order to reveal the reason for the difference between the photoelectrical properties of the two dyes, the ground state and excited state properties of the dyes before and after adsorbed on TiO2 were calculated via density functional theory DFT and time-dependent DFT TDDFT. The key parameters including the light harvesting efficiency LHE, the driving force of electron injection Δ G inject and dye regeneration Δ G regen , the total dipole moment μ normal , the conduction band of edge of the semiconductor Δ E CB , and the excited state lifetime τ were investigated, which are closely related to the short-circuit current density J sc and open circuit voltage V oc . It was found that the experimental carminic acid has a larger J sc and V oc , which are interpreted by a larger amount of dye adsorbed on a TiO2 photoanode and a larger Δ G regen , excited state lifetime τ, μ normal , and Δ E CB . At the same time, chemical reactivity parameters illustrate that the lower chemical hardness h and higher electron accepting power ω+ of carminic acid have an influence on the short-circuit current density. Therefore, carminic acid shows excellent photoelectric conversion efficiency in comparison with ethyl red. View Full-Text